What would your character use?
You can find metal, wood, ceramic, leather and probably other materials for cups and balls. Depending on what you are wanting to produce from the cups, and what look you prefer, you'll want different types of materials or designs of cups.
When I was writing my original routine out, I wanted to do a gag where I produced an elephant from the cup. So I went to a toy store with my cup and wandered around seeing if I could find an elephant that fit inside the cup.
These days the only time I use a cups and balls routine is when I'm doing my presentation on perceptual manipulation. Or if someone really begs me to. If I were to pick it back up I would, as I said, get a leather one because that suits the concept of my character more.
By the way, you can start learning the sleights with any cup. And though I don't particular like it myself, there is a routine that uses clear cups (Not P&Ts - but I'm blanking on the guy's name now - he does the laser act)